mmg_233_2013_genetics_genomicswikiaorg-20200214-history
Gallionella: Characterization of a Phenotype
Gallionella ferruginea ''is a gram-negative, microaerophilic chemolithotrophic bacteria. This particular genus has the ability to use Fe(II) as its sole energy source and carbon dioxide as its sole carbon source (1). It was discovered by Ehrenberg in 1836 and named after the French zoologist B. Gallion (1). The stalked structure present in some samples of Gallionella makes it easy to differentiate it from other types of bacteria. However, in the early 90's questions still remained about this bacteria since it was hard to culture. Isolation of Gallionella and generation of 16S rRNA primers Since Gallionella is hard to culture, samples were taken from a drinking water well and a special mineral salt solution containing iron sulphide was used to enrich for ''Gallionella (1)''. The cells were then harvested and concentrated. One of their samples contained a stalkless bacterium which survived under the same conditions that enriched for ''Gallionella but it was not known if it was Gallionella or another genus of iron oxidising bacteria (1). The advent of DNA sequencing through the use of the polymerase chain reaction (PCR) made this study by Hallbeck et al. (1993) possible. DNA and RNA was extracted from Gallionella using a phenol/chloroform/isoamyl alcohol extraction (1). The DNA was precipitated using ammonium acetate. PCR was then done to amplify this DNA. Sequencing of the DNA sequences was done immediately after PCR. This allowed the double stranded PCR product to be analyzed. Primers for conserved regions of the 16S rRNA gene were used (1). The hope was that unique 16S rRNA gene sequences could be amplified using the conserved primer sequences as a starting point. The sequences were then used to compare the known Gallionella sample with the sample from the unknown bacterium. Identification of the Unknown Bacterium Comparison of the unique 16S rRNA gene sequences derived from PCR for G. ferruginea' '''and the unknown bacteria, showed that it was indeed ''Gallionella that had a mutation which prevented it from forming stalks (1) . To further confirm this finding, both strains of G. ferruginea were grown under selective conditions. Both grew with ferrous carbonate as the energy source. At the time, there was a debate about whether or not G. ferruginea could use ferrous iron as a sole energy source (1). This experiment not only confirmed that both isolated strains were the same but it also supported the theory that G. ferruginea could utilize ferrous iron (1). Other experiments showed that both strains could use both ammonium and nitrate are nitrogen sources. It was previously known that Gallionella stalk formation occurs at pH < 6.0 (1), this paper presented evidence that strains of Gallionella ''might exist with the inability to form stalks at permissive pHs. The authors thought that this mutant would provide a good control for future experiments. The Importance of the Stalk Given that stalked and stalkless strains of ''G. ferruginea grow under the same conditions, does the stalk give some sort of advantage or is it not needed? Further experimentation with stalk and stalkless strains of G. ferruginea showed that the stalk confers protection against oxygen radicals (2). When stalk and stalkless strains were cultured in ferrous sulphide medium (gives rise to many toxic oxygen radicals), the stalked strain was able to survive longer than the stalkless strain (2). When samples of Gallionella were exposed to the air, stalks formed (2). This confirms that exposure to oxygen and the generation of oxygen radicals induces stalk formation as a method of sequestering these radicals. The stalks themselves are made of oxidised and precipitated iron. References 1. Hallbeck L, Ståhl F, & Pedersen K (1993) Phytogeny and phenotypic characterization of the stalk-forming and iron-oxidizing bacterium Gallionella ferruginea. Journal of General Microbiology 139(7):1531-1535. 2. Hallbeck L & Pedersen K (1995) Benefits associated with the stalk of Gallionella ferruginea, evaluated by comparison of a stalk-forming and a non-stalk-forming strain and biofilm studies in situ. Microbial ecology 30(3):257-268.